1. Field of the Invention
The present invention generally relates to an apparatus, to a driving mechanism that is provided in the apparatus in which the driving mechanism drives a particular element or component, and to a method for controlling the driving mechanism, and particularly relates to an optical apparatus including, for example, a camera and a binocular telescope, to the driving mechanism that is provided in the optical apparatus in which the driving mechanism drives, for example, an optical element of an optical system therein so as to compensate or correct a possible blur, caused at time of handing the optical apparatus, of image formed in the optical system by a feedback control, and to the method for executing the feedback control.
2. Description of the Related Art
Generally, when a precise control to drive a particular element or component is required in a driving mechanism of an apparatus in which the driving mechanism is provided, it has been practiced to execute a feedback control. In order to accurately execute the feedback control, it is very important to keep constant a cycle for carrying out the feedback operation. More specifically, the cycle therefor is gained, for example, by counting the number of signals output from an encoder to detect an operation of the driving mechanism, or by generating signals which synchronize with driving pulses to drive the driving mechanism. Alternatively, in order to more accurately keep constant the cycle for carrying out the feedback operation, it is possible to gain the cycle therefor by separately or independently measuring time by making use of a timer installed inside a microcomputer for controlling the driving mechanism. However, in case that such a timer is employed therein for the purpose, the overall construction and/or the control operation thereof becomes complex.
As an example, the aforementioned apparatus can be an optical apparatus including a camera and a binocular telescope. The driving mechanism can be the one that is provided in the optical apparatus in which the driving mechanism drives. For example, the optical apparatus could be an optical element like a correction lens (compensation lens) or a prism of an optical system therein that compensates or corrects a possible blur, which is caused at time of handing the optical apparatus, of an image formed in the optical system by the feedback control.
For example, the driving mechanism moves the lens, which is the optical element in the optical apparatus, in a direction to cancel the blur of an image formed in the optical system. The blur is caused at time of handling the optical apparatus.
More specifically, an amount of shaking of the optical apparatus and/or an amount of blur of the image formed in the optical system is/are detected by a variety of sensors installed in the apparatus while a position of the optical element, like the lens, is detected at predetermined timing. Based upon a result gained from the detection, a driving speed of the driving mechanism is newly sought for or calculated to execute the feedback control operation.
Next, referring to FIGS. 1 through 3, the following description provides an explanation about a driving mechanism in which there is provided an actuator employing an electromechanical transducer, such as a piezoelectric element the length of which changes (i.e. expands and contracts) when a voltage is supplied to the piezoelectric element.
This driving mechanism has a moving body 10 which can be moved relative to a base seat (stationary base) 1. Therefore, in a construction in which the moving body 10 is coupled to, for example, a lens frame for holding the correction lens (compensation lens), the lens held by the lens frame can be moved together with the moving body 10.
A reference numeral 4 denotes a piezoelectric element. The piezoelectric element 4 is made up of a number of piezoelectric plates which are laminated one over another. One end 4a of the piezoelectric element 4, in a direction in which the piezoelectric element 4 expands and contracts, is fixed to the base seat 1, whereas the other end 4b thereof, in the same direction, is fixed to an end 5a of a rod 5. The rod 5 is slidably supported by a pair of support portions 2 and 3, which are formed integrally with the base seat 1.
The moving body 10 has a body 11 and a cap 12 which cooperate together to sandwich the rod 5. The moving body 10 further has a pressure cap 13 which exerts a biasing force in a direction in which the rod is pinched between the body 11 and the cap 12, so that the moving body 10 is frictionally and slidably engaged around the rod 5.
The piezoelectric element 4 is electrically connected to an actuator driving circuit. When the actuator driving circuit continuously supplies a predetermined varying pulse voltage, like one with a sawtoothed wave-form 100, 100', 100" as shown in FIG. 3, the piezoelectric element 4 expands and contracts (i.e. vibrates) which in turn vibrates the rod 5.
More specifically, in correspondence with a gently ascending slope portion 101 of a first wave-form of the pulse voltage supplied by the actuator driving circuit, the piezoelectric element 4 expands slowly so that-the rod 5 also moves slowly in a direction shown by an arrow "A" in FIG. 2. Next, when the voltage is abruptly cut or reduced as shown by an abruptly falling cliff portion 102 of the first wave-form thereof, the piezoelectric element 4 abruptly contracts to return to its original length, so that the rod 5 also abruptly moves in a direction shown by an arrow "B" in the same figure.
When the pulse voltage is continuously applied to the piezoelectric elements 4 so that a plurality of waveforms 100', 100", and so on, similar in shape to the first wave-form 101 are repeated, the rod 5 vibrates so that it moves slowly in the direction shown by the arrow "A" and so that it moves rapidly in the direction shown by the arrow "B". The spring force of the pressure spring 13 of the moving body 10 (i.e. the frictional engagement force between the moving body 10 and the rod 5) is adjusted so that the moving body 10 moves together with the rod 5 relative to the base seat 1 as the rod 5 moves slowly, and so that the moving body 10 remains stationary, or moves a little bit, relative to the base seat 1 due to inertia of the moving body 10 as the rod 5 moves rapidly. Namely, while the rod 5 is vibrating as in the aforementioned manner, the moving body 10 moves in the direction shown by the arrow "A" relative to the base seat 1. Because the amplitude of the rod 5 during its vibration is very small, the amount of movement, relative to the base seat 1, of the moving body 10 corresponding to one pulse voltage (i.e. corresponding to each of the wave-forms 100, 100', 100", and so on) is also very small. Therefore, it is possible to control the position of the lens frame, holding the lens, that is connected to the moving body 10, with a high precision.
As a method for moving the moving body 10 in the direction shown by the arrow "B", opposite the direction shown by the arrow "A", in FIG. 2, an electric charge of the pulse voltage to be supplied to the piezoelectric element 4 can be reversed while maintaining the wave-form 100, 100', 100", and so on, of the voltage as shown in FIG. 3. With the application of the pulse voltage to the piezoelectric element 4, the piezoelectric element 4 slowly contracts for the gently ascending slope portion 101 of the wave-form of one pulse voltage, while the piezoelectric element 4 abruptly expands for the abruptly falling cliff portion 102 of the wave-form of the one pulse voltage to return to its original length of the piezoelectric element 4. The principle of movement of the moving body 10 in the direction shown by the arrow "B" is the same as the principle of movement of the moving body in the direction shown by the arrow "A" as explained above.
Next, the follwing description provides an explanation about how to compensate or correct a possible blur, which is caused at a time of handling the optical apparatus, of an image formed in the optical system of the apparatus. This compensation or correction is accomplished with the actuator in the driving mechanism and the actuator driving circuit explained above.
Generally, as explained above, it is of great importance to keep the feedback cycle constant in the feedback control. Accordingly, the feedback (i.e. application of a predetermined voltage to the piezoelectric element) must be executed every constant number of PWM (i.e. pulse-width modulation) pulses. That is, it is considered necessary to keep the feedback cycle constant, by independently or separately measuring time with a timer which is installed in a microcomputer.
Next, referring to FIGS. 8 and 9, the following description provides an explanation about how to carry out the feedback operation by an arrangement in which such a timer is installed in the microcomputer.
FIG. 8 illustrates an example in which the starting timing of the timer is synchronized with the PWM pulse (i.e. the starting point of the timer is made coincident with the starting point of the PWM pulse). For example, when the feedback operation is performed with a cycle corresponding to four PWM pulses as shown in the figure, the timer is set so that the timer will count up (i.e. the timer will stop measuring time) in a time shorter than the feedback period "4T" by a feedback processing time "ta", which is such a time required for the operation to actually change the actuator speed.
With the arrangement, the timer is started again so as to synchronize with the next PWM pulse, once after the feedback processing is done. This operation must be repeated every four PWM pulses corresponding to the feedback period "4T" as shown in the same figure. That is, the feedback control operation is complex, thus increasing the burden of the microcomputer other components.
Alternatively, FIG. 9 illustrates an example in which the starting timing of the timer is not synchronized with the PWM pulse (i.e. the starting point of the timer is not made coincident with the starting point of the PWM pulse). The timer is started earlier than the PWM pulse by the feedback processing time "ta".
In this arrangement, at time of starting the feedback control operation, it is necessary to calculate the time "ta" necessary for the feedback processing operation in advance, and to make the timer start earlier than the PWM pulse by the calculated time "ta". As a result, the control operation becomes complex at time of starting the feedback control, thus increasing the burden of the microcomputer other components, as well.